For people reading along, the crux of the matter is that MAME and the original cabinet draw the screen in a different direction. Here's a SO explanation of the implications behind that: https://retrocomputing.stackexchange.com/questions/8179/why-...

TL;DR MAME would have to emulate a CRT's electron beam drawing in the original cabinet's direction if it wanted to be spatiotemporally identical. The notion that a cabinet could glitch out and accidentally perfectly emulate MAME beggars belief.

Like you said, I suppose it could happen, in the sense that it wouldn't violate the known laws of physics.

But it didn't.